This invention relates to food mixing machines, more particularly to a vane system for drum-type tumble mixers operable under vacuum conditions and a chilling system for such machines.
Various meat products are tumbled under vacuum to improve the quality of the product. For example, poultry and ham are tumbled under full vacuum for approximately one hour to cause the product to absorb approximately 5-10% water and seasonings. The process makes the meat juicier, tenderer and more flavorful.
Drum tumble mixers for this purpose have much the same shape as concrete mixers but are designed to hold a full vacuum. Depending on the manufacturer, these drums have internal vanes approximately three to eight inches in height which, when the drum rotates, cause the produce to be lifted up with the vanes, with the product then spilling over the vanes. Since the product and water fill the drum about half full, the product will undergo a massaging action as the drum rotates. Thus, the product will be pressured and compressed as it is pushed ahead of the vanes, with the pressure being released as the product spills over the vanes. The compression of the product will squeeze air therefrom, while the release of pressure will allow the water and seasonings to be absorbed into the product. The effectiveness of the massaging depends on the height of the vanes and the level of vacuum. The higher the vanes, the more pressure is built up before the product flows over the tops of the vanes. The vane height, however, must be limited, since too high a vane will cause damage to the product, thus increasing waste. The higher the vacuum, the less reabsorption of air there will be when the pressure on the product is released.
Drum tumble mixers typically do not mix the product effectively from one end of the drum to the other. Most tumblers have vanes which are essentially parallel with the axis of the drum. Thus, the product rolls in a direction essentially perpendicular to the axis of rotation of the drum. When ingredients are added at the door on one end, they stay unmixed at that end. For this reason, the processor must often either pre-mix, or mix after vacuum tumbling. Neither alternative is acceptable, because extra mixing deteriorates and bruises the product and/or works air back into the product.
Rapid discharge is also critical since tumbling of the product after the vacuum is released will work air back into the product, thereby reducing quality. Vane configuration is critical to rapid discharge since the vanes massage the product when the drum is rotated in one direction and convey the product out the discharge door when the drum is rotated in the opposite direction.
The ideal tumble mixer is one which: (1) provides the optimum pressure fluctuations on the product as it is compressed and then tumbles over the vanes; (2) mixes the product completely from end to end in the tumbler drum, and; (3) discharges the product quickly from the drum when the vacuum is released and the discharge door is opened.
There are two basic types of vane systems presently used in vacuum tumblers: (1) spiral vanes, and; (2) parallel vanes. The spiral vane system uses a single vane which makes approximately two full rotations in the length of the tumbler drum. The parallel system has a multiple of vanes which are nearly parallel to the drum axis, but at a slight angle so as to provide a minimal conveying the product towards the discharge end of the drum when its rotation is reversed for discharge.
The main advantages of the spiral vane system are that, (1) it has a very fast discharge since the vane acts as a screw conveyor when the tumbler is reversed for discharge, and (2) it provides a very good end-to-end mixing of the product since the spiral vane tends to convey the product end-to-end during tumbling, causing it to flow end-to-end over itself. On the other hand, the spiral vane provides very poor massaging action since much of the product may slide along the vane instead of being compressed by the vane and then spilling thereover.
The parallel vane system has the opposite advantages and disadvantages. The pressure-pulsing massage is very good since there is very little movement of the product lengthwise of the tumbler during movement of the vanes. However, the limited movement of the product lengthwise of the drum results in poor end-to-end mixing. The vacuum tumbler will discharge fairly rapidly from its single discharge trough when the tumbler is nearly full. However, when the tumbler approaches one quarter full, the rate of discharge is reduced dramatically because the discharge trough can only pick up the product that has finally reached the discharge end of the drum. The slow end-to-end movement of the product caused by the vanes thus requires substantial time to move the remainder of the product into position for discharge.
In the processing of most meat and poultry products, it is desirable to chill the product after vacuum tumbling. In the past, when a food product has been processed in a tumble mixer, it has been necessary to remove the product from the vacuum tumbler and convey it into a twin agitator blender equipped with CO.sub.2 (carbon dioxide) snowhorns. A CO.sub.2 snowhorn is a cylindrical tube, open at one end and closed at the other, with a liquid CO.sub.2 injection nozzle in the closed end. Liquid CO.sub.2 is injected and swirled inside the tubular horn, causing it to turn into CO.sub.2 snow. This snow is ejected from the horn into the blender chamber and is mixed with the product. As the snow sublimates into gas, it chills the product in which it has been mixed.
The present chilling systems have several significant problems. First of all, the need to transfer the product from the vacuum tumbler to the blending machine requires more time in the processing of the product. Secondly, the CO.sub.2 blenders in use today may cause considerable damage to the meat fibers of the poultry products, particularly when the product is chilled.
As a consequence, there is a need to provide a way to chill the product quickly and with a minimum of mechanical damage to the product.
Two factors must be taken into consideration in determining the cost of chilling a product, namely the efficiency of generation of CO.sub.2 snow and the efficiency of mixing the CO.sub.2 with the product that is to be chilled. Liquid CO.sub.2 is very expensive and it is very desirable to use the least amount of liquid CO.sub.2 to provide the desired amount of chilling.
As is well known in the art, there is a combination of snowhorn diameter, length, orifice diameter, number of orifices and rate of flow of liquid CO.sub.2 to the snowhorn that will convert liquid CO.sub.2 into CO.sub.2 snow most efficiently. If one of these parameters is changed without adjusting the other parameters, the snow generating efficiency of the horn will be reduced. That is, the number of ounces of snow that can be generated from pound of liquid CO.sub.2 will be decreased, and the cost of chilling will be increased.
From the moment that CO.sub.2 snow is formed, it will begin to change into a gas. This change of state from a solid snow to a gas requires significant heat; thus, products with which the snow is in contact are chilled. If the snow is not evenly mixed with the product as it changes state, it will unevenly chill the product. If the snow is being generated at a greater rate than the snow can be mixed into the product, the excess snow will merely chill the air around the product as it subliminates, and the chilled air will be pushed out of the CO.sub.2 discharge vent without an effective chilling of the product.
The efficiency of mixing the CO.sub.2 snow into the product depends on the design of the mixer--the vane design in the case of a tumbler, or the agitator design in a blender. The mixing efficiency also depends on the nature of the product being blended. This presents a very difficult engineering and food processing problem. The design of an efficient snowhorn system cannot be readily changed to adjust the rate of snow generation to the rate at which the snow can be mixed with the product without adversely affecting the efficiency of the snowhorn. In addition, the easiest parameter that can be changed is the orifice, but the changing of the orifice takes considerable time and the result is difficult to anticipate. Thus, this becomes a trial-and-error process. Likewise, it may be very difficult or impracticable to change the efficiency of mixing so that all of the produced snow is mixed with the product. For example, the efficiency of mixing could be increased by rotating the tumbler drum or agitator vanes at a higher speed. However, this may increase the damage to the product to an unacceptable level.
As a consequence there is a need to provide a way of producing CO.sub.2 snow with high efficiency and with the rate of production being matched to the rate at which the snow can be efficiently mixed with the product.